Climatic features of Siberia and Polar North regions make it necessary to store the supplies of raw materials at working sites designed for a year. Long-term storage, even under favourable conditions, results in consolidation of cement and loss of its activity. Cement properties are materially impaired upon a long-term storage under unfavourable conditions, and especially during the autumn and winter period: cement is partly hydrated, lumped, setting time of cement mortar becomes longer, viscosity increases, cement stone strength properties are deteriorated and cement becomes unsuitable for grouting of wells.
Many types of equipment are now developed for the improvement of activity of binder materials prior to their use, which are based on mechanical activation using various mills, hydrycyclones, turbines, as well as vibratory, electromagnetic, ultrasonic and the like arrangements.
Known in the art is an apparatus for the activation of cement (cf. U.S. Pat. No. 3,987,967, Cl. 241-1), comprising at least one electromagnetic particle size reducer with a common reducer hopper at the inlet ensuring a gravity feeding of cement to the reducer.
The apparatus also comprises a series sequence including a receiving hopper with a crusher, a conveying screw in a casing, a classifier at the end of the screw comprising a flat screen with a frame arranged in a casing, an accumulating hopper having its inlet communicating with the classifier casing and the outlet communicating with the reducer hopper.
The screw and classifier of the apparatus have individual drives and a common control device so as to ensure a continuous flow of cement from the receiving hopper to the outlet of the electromagnetic reducer.
The electromagnetic reducer of the apparatus has a working chamber made of a non-magnetic material which is closed by a screen at the outlet for retaining working bodies made of magnetized magnetically hard pellets, such as barium hexaferrite pellets.
The working chamber of the reducer is surrounded by an electromagnetic coil supplied from an alternating current supply mains, and under the action of electromagnetic field of the oil the magnetized working bodies move chaotically to comminute, abrade and stir cement particles.
Combination of mechanical and magnetic actions in the prior art apparatus contribute to more complete restoration of active properties of cement.
The apparatus is designed for operation under stationary conditions in a production workshop manufacturing either cement or finished concrete products since the provision of several individual drives, devices taking no part in the activation process and functioning as auxiliary conveying means, as well as passive intermediate arrangements make the design complicated and cumbersome and do not enable the mobility of the apparatus for operation at construction and drilling sites where cement is directly used.
Moreover, in order to ensure continuous and uniform transportation of cement along all ducts of the apparatus, a device for an additional mechanical action on all passive intermediate arrangements--hoppers--is required, which also complicates the apparatus.
Known apparatus for the activation of cement is complicated in operation since it requires a continuous control for matching the output of various arrangements. Thus, when the starting cement physico-mechanical properties change, there is a mismatch in the operation of the receiving hopper, crusher and classifier arranged at the outlet of the screw. In particular, in case the moisture content of the starting cement increases, the output of the crusher also increases, and the output of the classifier decreases.
And finally, the prior art apparatus lacks uniformity of cement flow through the electromagnetic reducer which is due to the absence of an automatic cement level control at the inlet hopper of the electromagnetic reducer.
This lack of uniformity of cement flow through the working chamber effects the degree of activation of cement in the electromagnetic reducer and lowers the durability of the reducer and in certain instances results in an interruption of the reducer operation.